Research On Uplink And Downlink Wireless Access Technology In IoT Scenarios

In recent years,the development and rise of various Internet of Things applications have gradually changed people's lives.The country also vigorously promotes the construction of industrial Internet of Things.All above indicates that the era of Internet of Things is coming.The key to the construction of the Internet of Things is the communication between machines.Ensuring the efficient and stable access between Internet of Things equipment is the premise of realizing the interconnection of all things.However,the existing wireless access technology is mainly designed to adapt to human voice communication,which cannot fully meet the growing needs of Internet of Things scenarios.Therefore,the uplink and downlink wireless access technology of Internet of Things is studied in this thesis.The specific research work is as follows:Firstly,to address the problem of frequency offset in downlink timing synchronization,the influence of frequency offset on timing synchronization is specifically analyzed.The downlink synchronization signal structure based on conjugate sequence is designed creatively.The principle of how the proposed synchronization signal structure eliminate the effect of frequency offset is derived.In addition,the generation method of frequency offset tolerant sequence is analyzed.In this way,the frequency offset tolerant ability of downlink timing detection is improved effectively.The performance loss of timing detection is about 2 d B when the largest frequency offset is 40 k Hz.Secondly,to address the problem of quantization errors caused by low sampling rate in narrowband system,which will affect timing accuracy,optimization method based on parabola curve fitting is proposed based on traditional timing detection algorithm.The discrete points of the direct correlator output curve are used for curve fitting to recover the real peak of the correlator output at low sampling rate.In this way,the timing accuracy is improved with low complexity.The performance of the optimization method based on parabola curve fitting with two times the rate of the Nyquist sampling rate is close to traditional timing algorithm with sixteen times the rate of the Nyquist sampling rate.Finally,to address the problem of random access management in massive machine type connection,the system model of uplink access and data transmission is established.The specific expressions of two key system parameters are derived,including the mean time length of each connection and the resource utilization ratio.On this basis,considering signaling overhead,access delay and resource utilization,an optimization algorithm based on maximizing system utility is proposed.The optimal duration for RRC to stay connected when there is no data transmission is obtained.In this way,the system utility is maximized.